Firewater Runoff Management and Fire Risk Mitigation for BESS: Best Practices for Environmental Protection

You have probably heard the stories about the lithium-ion batteries in mobile phones and electric cars overheating and bursting into flames. There is a reason large portable power banks are not allowed in checked luggage on planes.

Now imagine that on a much larger scale.

That is the danger posed by Battery Energy Storage Systems (BESS) that are being built at an exponential rate across the world. Incidents may be rare, but preparedness is essential.

What is BESS?

Battery Energy Storage Systems (BESS) are essentially large-scale batteries that store electrical energy and release it when needed. They are a key part of modern electricity grids and renewable energy setups, such as solar and wind farms, because they help balance supply and demand, store excess renewable energy, and provide backup power.

However, there is a non-trivial fire risk associated with large-scale BESS, and there have been several notable incidents recently. The biggest risk with lithium-ion batteries is thermal runaway: a cell overheats, triggers a chain reaction, and adjacent cells also heat up, potentially leading to a large fire or explosion. Causes of thermal runaway can include manufacturing defects, physical damage, poor thermal management, overcharging, or a failure of the Battery Management System (BMS).

What Are the Additional Fire Risks Associated With Bess?

BESS fires can be extremely hard to put out. Traditional firefighting techniques may be ineffective, and fires can re-ignite, even after they appear to be extinguished. This is one of the reasons why firefighters in Moss Landing, California, allowed parts of the fire that occurred in January 2025 to burn out rather than aggressively fighting it. According to the UK National Fire Chiefs Council (NFCC), water can struggle to penetrate battery cells, meaning thermal propagation (fire spreading between cells) can continue. Run-off from firefighting water can also become contaminated, raising environmental concerns.

A critical danger is propagation, where fire spreads from one cell/module to others, potentially triggering a cascade. Containment design is therefore especially important: how battery modules are grouped, how racks are spaced, containment structures, and thermal management all matter for reducing risk.

Fire services and regulators are warning that the rapid growth of “battery farms” (large BESS sites) is an “emerging risk.” There are concerns about how some BESS sites are being planned, especially in dense or residential areas. A survey found that around 26% of battery storage systems inspected had issues with fire detection or suppression systems, meaning not all sites are equally well protected.

In the UK, the NFCC warns that although BESS failures are rare, when they do happen they can be very challenging: “ these batteries…can pose a significant fire risk due to thermal runaway.” There was a BESS fire in Essex in February 2025. According to Essex County Fire & Rescue, it required a large response. The blaze took almost 24 hours to extinguish, raising alarms about response capabilities in the UK. Another BESS fire in Liverpool in 2020 lasted three days.

Concerns Around the Location of BESS Sites

Many BESS sites are near sensitive infrastructure, homes, or environmental zones. New York City councillor, Robert Holden, is reported by the BBC to have said, “It makes absolutely zero sense why, now, these facilities are being sited practically in people’s backyards, and next to gas stations, all over Staten Island.”

“Simply put, it is not just a bad policy, but a dangerous one, and the city is literally playing with fire by allowing this to happen.”

Residents living near proposed BESS sites are strongly opposing the planning proposals and actively voicing their concerns. Campaigner, Marguerite Fleming, who lives in Aberdeenshire, told the BBC, “They don’t have any consideration for the residents that live outside their red line around their property, they don’t take the residents into consideration for flood risk or fire.”

A spokesperson for Blackford Renewables, the company behind the Aberdeenshire proposal, said, “We take local concerns about fire safety very seriously, and we are committed to maintaining the highest safety standards through the use of advanced technology, fire safety systems and close coordination with emergency services.”

What is the Industry Doing to Mitigate the Fire Risks?

To reduce the fire risk associated with BESS, industry and safety bodies are emphasising several mitigation and safety strategies:

• Design and containment measures such as using modular units, better thermal management, spacing, insulation and compartmentalisation can help prevent a failure in one module from cascading into neighbouring units, improving overall safety and reducing fire propagation risk.
• Improved fire detection and suppression systems are critical: integrating early-warning sensors (e.g., multi-parameter detectors for smoke, gas and heat) along with robust suppression systems (often water-based systems shown to be effective for lithium-ion fires) and bespoke emergency response plans enhances both early detection and firefighting capability.
• Engagement with fire and rescue services early in planning and design ensures that emergency responders understand the site layout, risks and mitigation systems, helping align developer plans with practical firefighting strategies. 
• Regulatory and planning safeguards such as stricter siting guidance, comprehensive risk assessments and community consultation help ensure facilities are located and designed with appropriate safety and environmental considerations, consistent with advice from the UK’s National Fire Chiefs Council (NFCC).
• Effective post-incident management — including careful removal and safe disposal of damaged batteries after a fire, monitoring for potential reignition, and environmental remediation — is essential to prevent further risk and contamination, as highlighted by regulatory oversight following the Moss Landing BESS fire in California.

The Often Overlooked Risk: Firewater Run-Off

It is not only the fire itself that poses a risk. The potential of contaminated firewater run-off cannot be ignored. Firewater from BESS fires can contain heavy metals, chemicals, and debris, creating both a safety and environmental hazard with contamination risks to local drains, watercourses, groundwater, and wildlife.

If contaminated firewater causes a pollution incident, there are regulatory implications, including pollution offences and cleanup costs. Plus, you cannot forget the associated reputational damage that could hit a business’ bottom line.

The Importance of Drain Closure Systems

Having effective controls to contain firewater during a rare BESS fire is crucial for preventing contaminated water from harming the environment. Drain closure systems help by stopping polluted firewater from escaping through the site’s drains, keeping it contained until experts can safely remove it. These systems not only protect the environment but also lower liability risks and aid emergency services.

How Drain Closure Complements Wider Safety Measures

Drain closure systems are a vital component in the layered safety strategy required for BESS facilities. They work alongside other key measures such as electrical isolation, fire suppression systems, and environmental containment protocols to form a comprehensive risk management framework. By automatically sealing drains during an incident, these systems prevent contaminated firewater from escaping the site, thereby containing hazardous substances and protecting neighbouring environments.

• Forms part of a holistic approach: Drain closure can be integrated with electrical isolation, which ensures that power supplies are safely shut off during emergencies; fire suppression systems, which quickly control and extinguish fires; and robust environmental containment, which includes bunds and barriers to stop the spread of pollutants. This constructive collaboration ensures that if a fire or leak occurs, all aspects, from immediate fire control to long-term environmental protection, are addressed.
• Provides peace of mind for stakeholders: The presence of drain closure systems reassures operators, site planners, insurers, and regulators that robust controls are in place to mitigate pollution risks. Knowing that contaminated firewater can be effectively contained reduces liability concerns and demonstrates a proactive commitment to regulatory compliance and environmental stewardship. This can also be a positive factor in obtaining permits, reducing insurance premiums, and maintaining the facility’s reputation.
• Supports emergency response: During a fire or spill, emergency services benefit from having drain closure mechanisms in place, as they can focus on managing the incident without worrying about immediate offsite contamination. It also enables a controlled cleanup process, minimising the risk of secondary environmental impacts.
• Aligns with Best Available Techniques (BAT): Incorporating drain closure aligns with BAT guidelines, which recommend using the best technologies and practices to prevent water pollution. This approach ensures that containment and pollution control are embedded into site design and operation from the outset, not just as an afterthought.

By making drain closure systems a standard part of BESS safety planning, operators demonstrate a commitment to comprehensive risk reduction — protecting people, property, and the environment while maintaining regulatory and community trust.

Bund Dewatering – Preventing Oily Discharge into Watercourses

Many BESS installations use bunds to contain transformers, switchgear, or auxiliary equipment. Rainwater collects in bunds and must be emptied safely. Bund dewatering units automatically drain clean water while blocking oil, fuel, and contaminants. This prevents pollution, supports permit compliance, and maintains bund capacity for safe containment of leaks.

Bund dewatering is a critical part of environmental management at BESS sites and other facilities using hazardous liquids. Without effective dewatering, accumulated rainwater can reduce the capacity of bunds, increasing the risk that spills or leaks will overflow and reach the environment.

Automated bund dewatering systems are fitted with sensors and filtration media designed to distinguish between uncontaminated water and harmful substances like oil or fuel. If contamination is detected, the system halts discharge and contains the pollutants within the bund for proper disposal. Proper maintenance and regular inspection of these units are important to ensure their reliability and ongoing compliance with regulatory requirements. Inadequate bund dewatering practices can result in costly environmental incidents, legal penalties, and reputational damage for operators.

Ensuring Sustainable and Safe BESS Operations

BESS plays a vital role in accelerating the transition to renewable energy sources. While fire risks associated with these installations are genuine, they can be effectively managed through robust systems and proactive planning, significantly minimising the likelihood and impact of incidents.

Environmental protection must be at the forefront of responsible BESS operation. This includes critical measures such as firewater containment and bund dewatering, which safeguard both the site and the surrounding environment from potential contamination. Implementing automated bund dewatering and reliable drain closure mechanisms not only helps sites comply with regulations but also demonstrates a genuine commitment to environmental stewardship and community safety.

We strongly encourage operators, developers, and consultants to integrate drain closure and runoff containment into their overall safety strategies. By making these systems standard practice, stakeholders ensure comprehensive risk reduction, protect people and property, and maintain the trust of regulators and the public.

Planning for these controls from the outset is essential for building resilient, future-ready BESS facilities that support the broader goals of sustainability and clean energy.